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The Latest Research Items

Most Read Articles of 2013

An article titled "Catalytic Hydrotrifluoromethylation of Styrenes and Unactivated Aliphatic Alkenes via an Organic Photoredox System," published in the journal Chemical Science by Professor David Nicewicz, his postdoctoral assistant Dale Wilger, and graduate student Nathan Gesmundo, has been listed as one of the 25 most read articles of 2013.

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Chemical Science is the Royal Society of Chemistry's flagship journal, publishing research articles of exceptional significance and high-impact reviews from across the chemical sciences. Research in Chemical Science is not only of the highest quality but also has excellent visibility.

 

Colloidal Plasmonic Copolymers

Professor Michael Rubinsten is one of the authors of an article featured on the cover of Angewandte Chemie, discussing how the resemblance between colloidal and molecular polymerization reactions is very useful in fundamental studies of polymerization reactions, as well as in the development of new nanoscale systems with desired properties. Future applications of colloidal polymers will require nanoparticle ensembles with a high degree of complexity that can be realized by hetero-assembly of NPs with different dimensions, shapes, and compositions.

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The article describes how a method has been developed to apply strategies from molecular copolymerization to the co-assembly of gold nanorods with different dimensions into random and block copolymer structures, plasmonic copolymers. The approach was extended to the co-assembly of random copolymers of gold and palladium nanorods. A kinetic model validated and further expanded the kinetic theories developed for molecular copolymerization reactions.

 

Fluorous Enzymatic Synthesis

As presented in Chemical Communications, researchers in the Allbritton Group in collaboration with Qisheng Zhang, associate professor in UNC's School of Pharmacy, and his group, have published a fluorous tagging strategy coupled with enzymatic synthesis to efficiently synthesize multiple phosphatidylinositides (PIs). PIs and their derivatives are notorious for their structural complexity, with seven stereogenic centers and the hydroxyl groups around the inositol head unit having similar reactivity.

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Most synthetic strategies require selective protection and deprotection of the hydroxyl groups, and usually take more than 15 steps to synthesize one PI. The work presented by the two groups introduces "fluorous enzymatic synthesis," where tandem enzymatic reactions are used to generate multiple probes after purification through fluorous solid phase extraction. These probes can then be used as enzyme reporters, or be directly immobilized on a fluorous surface to form a microarray to investigate protein-small molecule interactions. This strategy should also be applicable to other complex endogenous small molecules whose biosynthetic enzymes are well characterized.

 

Tunable Fluorescent Reporters

In vivo optical imaging must contend with the limitations imposed by the optical window of tissue, 600–1000 nm. Although a wide array of fluorophores are available that are visualized in the red and near-IR region of the spectrum, with the exception of proteases, there are few long wavelength probes for enzymes. This situation poses a particular challenge for studying the intracellular biochemistry of erythrocytes, the high hemoglobin content of which optically obscures subcellular monitoring at wavelengths less than 600 nm.

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To address this, researchers in the Lawrence Group, published in Angewandte Chemie, developed tunable fluorescent reporters for protein kinase activity. The probing wavelength is preprogrammed by using readily available fluorophores, thereby enabling detection within the optical window of tissue, specifically in the far-red and near-IR region. These agents were used to monitor endogenous cAMP-dependent protein kinase activity in erythrocyte lysates and in intact erythrocytes when using a light-activatable reporter.

 

Self-Healing Polymer Networks

Self-healing polymeric materials are systems that after damage can revert to their original state with full or partial recovery of mechanical strength. Using scaling theory, researchers in the Rubinstein Group, as published in Macromolecules, studied a simple model of autonomic self-healing of unentangled polymer networks. In this model one of the two end monomers of each polymer chain is fixed in space mimicking dangling chains attachment to a polymer network, while the sticky monomer at the other end of each chain can form pairwise reversible bond with the sticky end of another chain. The group studied the reaction kinetics of reversible bonds in this simple model and analyzed the different stages in the self-repair process.

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The team observed the slowest formation of bridges for self-adhesion after bringing into contact two bare surfaces with equilibrium, very low, density of open stickers in comparison with self-healing. The primary role of anomalous diffusion in material self-repair for short waiting times is established, while at long waiting times the recovery of bonds across fractured interface is due to hopping diffusion of stickers between different bonded partners. Acceleration in bridge formation for self-healing compared to self-adhesion is due to excess nonequilibrium concentration of open stickers. Full recovery of reversible bonds across fractured interface, formation of bridges, occurs after appreciably longer time than the equilibration time of the concentration of reversible bonds in the bulk.

 

Face-to-Face Molecules

New research from the You Group, in collaboration with researchers at NCSU, reveals that energy is transferred more efficiently inside of complex, three-dimensional organic solar cells when the donor molecules align face-on, rather than edge-on, relative to the acceptor. This finding may aid in the design and manufacture of more efficient and economically viable organic solar cell technology.

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The paper appears online in Nature Photonics. Fellow NC State collaborators were John Tumbleston, Brian Collins, Eliot Gann, and Wei Ma. Liqiang Yang and Andrew Stuart from UNC-Chapel Hill also contributed to the work. The work was funded by the U.S. Department of Energy, Office of Science, Basic Energy Science, the Office of Naval Research, and the National Science Foundation.

 

Platinum Catalyzation

The biomimetic cyclization of polyene containing substrates to their polycyclic counterparts has long benefitted from the installation of highly nucleophilic terminating groups. The more challenging bio-like alkene terminating substrates have received considerably less attention.

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Research in the Gagné Group published in the Journal of the American Chemical Society has detailed the Pt catalyzed cycloisomerization of strictly polyene containing substrates to polycles. Cyclization of acyclic polyene substrates to bi, tri and tetracyclic products is observed, forming up to five stereocenters in a single step.

 

Biodegradable Memory

Assistant Professor Scott Warren, a joint faculty member with the Department of Chemistry and the Applied Physical Sciences Department here at UNC, is one of the co-authors of an article, published in Angewandte Chemie, describing how single crystals of a cyclodextrin-based metal–organic framework, MOF, infused with an ionic electrolyte and flanked by silver electrodes act as memristors. The article is highlighted in ChemistryWorld, where the invention is referred to as "Computer Memory Made From Sugar Cube."

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Tony Kenyon, an electronic engineer at University College London, says the sugar-cube memory’s performance would not be compatible with existing complementary metal oxide semiconductor, CMOS, technology, the staple of modern computing. But he also points out that other applications could be very interesting. The authors comment that commercial RRAMs have faster read and write times, but state they believe they can make this type of memory cheaper and most definitely greener. The researchers are thinking along the lines of "biodegradable memory."

 

Response of Single Leukemic Cells

Single-cell methodologies are revealing cellular heterogeneity in numerous biological processes and pathologies. For example, cancer cells are characterized by substantial heterogeneity in basal signaling and in response to perturbations, such as drug treatment. In an article published in Integrative Biology, members of the Allbritton Group examined the response of 678 individual human acute myeloid leukemia cells to an aminopeptidase-inhibiting chemotherapeutic drug, Tosedostat, over the course of 95 days. Using a fluorescent reporter peptide and a microfluidic device, they quantified the rate of reporter degradation as a function of dose. While the single-cell measurements reflected ensemble results, they added a layer of detail by revealing unique degradation patterns and outliers within the larger population.

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Regression modeling of the data allowed us to quantitatively explore the relationships between reporter loading, incubation time, and drug dose on peptidase activity in individual cells. Incubation time was negatively correlated with the number of peptide fragment peaks observed, while peak area, which was proportional to reporter loading, was positively correlated with both the number of fragment peaks observed and the degradation rate. Notably, a statistically significant change in the number of peaks observed was identified as dose increased from 2 to 4 μM. Similarly, a significant difference in degradation rate as a function of reporter loading was observed for doses ≥2 μM compared to the 1 μM dose. These results suggest that additional enzymes may become inhibited at doses >1 μM and >2 μM, demonstrating the utility of single-cell data to yield novel biological hypotheses.

 

Ex Vivo Quantification of PTP

Published in Analytical Chemistry, scientists in the Allbritton Group in collaboration with colleagues from Pharmacology, Biostatistics and Endodontics, and Biomedical Engineering, all at UNC, and the National Health and Environmental Effects Research Laboratory, describe a novel method for the measurement of protein tyrosine phosphatase, PTP, activity in single human airway epithelial cells, hAECs, using capillary electrophoresis.

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Their technique involved the microinjection of a fluorescent phosphopeptide that is hydrolyzed specifically by PTPs. Initial results were then extended to a more physiologically relevant model system: primary hAECs cultured from bronchial brushings of living human subjects. The results demonstrate the utility and applicability of this technique for the ex vivo quantification of PTP activity in small, heterogeneous, human cells and tissues.